The following correction was printed in the Guardian's Corrections and clarifications column, Tuesday February 12 2008

The headline on this article about research into child obesity wrongly said a US study had found a genetic link. It was a British study, although the results were published in an American journal. This has been corrected.

A study of more than 5,000 pairs of twins has found that a child's risk of becoming overweight is mostly down to nature, not nurture. The research into children aged between eight and 11 showed that the variation in a child's body mass index and waist circumference was 77% attributable to genes and 23% to the environment in which they grow up.

Overweight children are more likely to become overweight or obese adults, a condition that can contribute to ill health and increased cancer risk in later life. The results are published today in the American Journal of Clinical Nutrition.

"This study shows that it is wrong to place all the blame for a child's excessive weight gain on the parents; it is more likely to be due to the child's genetic susceptibility," said Jane Wardle of University College London.

A twin study allows scientists to work out the extent of the genetic contribution to a pattern of behaviour compared with the environmental contribution.

Identical twins, who share all their genes, are compared with non-identical twins, who share half their genes. By spotting behaviour or traits that occur more often in identical rather than non-identical ones, scientists can work out the relative contribution of genetics.

Study author Susan Carnell, a psychologist at University College London, said that genetically influenced behaviour was not inevitable. "One of the ways genes could be acting is through behaviour, ie food intake and physical activity, and these things are under our conscious control. Genes just might make it more difficult for some people than others."

Sara Hiom, Cancer Research UK's director of health information, said: "This research highlights the importance of doing all we can to encourage children to eat healthily.

"If genetic influence is strong, we must try to counter these inherited tendencies by providing the healthiest possible environment, and educating parents on the importance of a well-balanced diet and an active lifestyle."